Curable compositions of epoxy resins and 4,6-bis(substituted carbamyl)isophthalic acid

ABSTRACT

4,6-Bis (substituted carbamyl) isophthalic acid compounds are used as latent hardeners for epoxy resins materials the cured resins therefrom are employed in high-temperature adhesives and coating applications. The hardener effect is achieved by curing at elevated temperatures.

United States Patent [72] Inventors RaymondMichaelMoran,Jr.

Brick Town; Robert Paul Kretow, Lakewood, both of NJ.

211 App]. No. 868,924

[22] Filed Oct. 23, 1969 [45] Patented Dec. 14, 1971 [73] Assignee CibaCorporation Summit, NJ.

[54] CURABLE COMPOSITIONS OF EPOXY RESINS AND 4,6-B1S(SUBST1TUTEDCARBAMYLflSOPl-ITHALIC ACID 3 Claims, No Drawings [56] References CitedUNITED STATES PATENTS 3,140,299 7/1964 Loncrini 260/47 Ep X OTHERREFERENCES E. l. du Pont de Nemours & Co. Bulletin PMDA/P- MA6/l 960(page 5 Chemical Abstracts, Vol. 64 (12807D) 1966 PrimaryExaminer-William H. Short Assistant Exam inerT. Pertilla Attorneys-HarryGoldsmith, Joseph G. Kolodny and Mario A. Monaco ABSTRACT: 4,6-Bis(substituted carbamyl) isophthalic acid compounds are used as latenthardeners for epoxy resins materials the cured resins therefrom areemployed in hightemperature adhesives and coating applications. Thehardener effect is achieved by curing at elevated temperatures.

C URABLE COMPOSITIONS OF EPOXY RESINS AND 4,6- BIS(SUBSTITUTEDCARBAMYL)ISOPI-ITIIALIC ACID BACKGROUND OF THE INVENTION This inventionrelates to the curing of epoxy resins. More particularly, it relates tothe discovery of a class of compounds useful in the curing of epoxidesto produce materials useful as high-temperature adhesives, castings,moldings and powder coatings.

I There are a great many forms of epoxide resins available today, manyof which can be cured by various means to provide final productstailored to a specific end use: Thus, solid, infusible resins have beenprepared in this manner using a variety of amines as curing agents.Similarly, soft, flexible products have been obtained using certainmetal salt as a curing agent for some polyepoxides.

Epoxy systems normally are comprised of at least two compounds, one ofwhich is the epoxy resin, and the other a hardener. Prior to use, thesecomponents must be stored separately, to prevent reaction to a cured orinfusible state. In the production of cured epoxides, it is sometimesdesirable to provide a mixture which will not cure under normal ambientconditions, but will remain as a stable blend for a reasonable I periodof time. Activation of such a mixture to a cured state,

desirably, is then achieved by curing at an elevated temperature. Themixture should have a cure time at an elevated temperature that will notbe oppressive from an economic point of view, but should not be so rapidas to prevent adequate work ing time. In addition to thesecharacteristics, the resulting cured product should possess goodphysical and mechanical qualities so as to function in an acceptablemanner. The. art has not been altogether successful in achieving theseresults for various reasons. Thus, while a stable resin/hardener mixturemay be obtained, the resulting blend is not always curable underreasonable conditions of time and temperature. Often, if curable, theblend is not cured to an entirely suitable state. Therefore, the art iscontinuously searching for new and improved hardener materials.

A new class of compounds has now been discovered which when blended withvarious epoxides results in a relatively sta ble mixture under normalconditions, but which because of latent hardening capabilities, exerts a.curing effect on the epoxides at elevated temperatures. Such compoundsmay be described as 4,6-bis (substituted carbamyl) isophthalic acidshaving the formula HOOC COH RNOC 0 ONE H H wherein R is an amino-bearingphenyl, benzyl, cyclohexyl, or cyclohexylmethyl radical. Moreparticularly, R is either wherein n is 0 or I, and R and R, arehydrogen, alkyl, amino, alkyl-amino, alkoxy, and heterocyclic systemcontaining a heteronitrogen atom carrying an active hydrogen; providedhowever that R and R are not at the same time hydrogen and provided thatat least one ofsaid R and R substituents is amino or amino-bearing.Preferred groups are amino, methyl, ethyl, aminomethyl, aminoethyl,aminopropyl, benzimidazolyl, methoxy, ethoxy, propoxy, and pyridyl, andthe like. The most preferred compound is not wherein R is 2-aminophenyl. Other illustrative compounds are:

4,6 bis [(3-aminomethyl, cyclohexylmethyl)carbamyl] isophthalic acid,

4,6 bis (3-aminophenyl carbamyl) isophthalic acid,

4,6 bis [(3-aminomethyl phenyl)carbamyl] isophthalic acid,

4,6 bis [(4-methoxy-6-aminophenyl)carbamyl] isophthalic acid,

4,6 bis l -methyl-4l2-amino-isopropyllcyclohexyl) carbamyl isophthalicacid, and

4,6 bis [(4-benzimidazolyl phenyl)carbamyl] isophthalic acid.

The foregoing latent hardeners demonstrate their capability whenemployed with a wide variety of epoxy compounds. Various conditions ofcure time and temperature, and the physical properties of the curedresin will, of course, vary from compound to compound. In general,however, the epoxy compounds to be cured are those possessing more thanone epoxide group and may carry inert substituents such as chloro andother well known and encountered in the art, and may be monomers orpolymeric. They also contain ether linkages and ester groups as well.Especially preferred are epoxides prepared from Bisphenol A, a phenol orcresol and epichlorhydrin, although virtually any epoxide produced froma polyhydric alcohol and epichlorhydrin may be used. Preferably,epoxides having an epoxy value of 0.40-70 equivalent per 100 gm. ofmaterial are suitable. Typical epoxides are those produced fromepichlorhydrin and a polyhydric phenol or alcohols such as resorcinol,catechol, l,2,6-hexanetriol, sorbitol, mannitol pentaerythritol,trimethylolpropane, glycerol allyl ether. Similarly, polymeric materialscontaining polyhydric hydroxyls such as appropriately substitutedpolyethers and polyesters may likewise be employed. For example, theremay be employed vinyl cyclohexene dioxide, epoxidized mono-, diandtriglycerides, butadiene dioxide, l,4-bis(2,3-epoxypropoxy)benzene,l,3-bis(2,3-epoxypropoxy)benzene, 4,4'-bis(2,3-epoxypropoxy)diphenylether, l,8-bis-(2,3-epoxypropoxy)octane,l,4-bis(2,3-epoxypropoxy)cyclohexane,4,4-bis(2-hydroxy-3,4-epoxybutoxy)diphenyldimethylmethane,l,3-bis(4,5-epoxypentoxy)-5- chlorobenzene, l,4-bis(3,4-epoxybutoxy)2-chlorocyclohexane, diglycidyl thioether, diglycidyl ether, ethyleneglycol diglycidyl ether, resorcinol diglycidyl ether,l,2,5,6-diepoxyhexyne-3, l,2,5,6-diepoxyhexane, and l,2,3,4,-tetra-(2-hydroxy-3,4-epoxybutoxy)butane. 1

Other examples include the glycidyl polyethers of polyhydric phenolsobtained by reacting a polyhydric phenol with an excess, e.g., 4 to 8mol excess, ofa chlorohydrin, such as epichlorohydrin and diglycerolchlorohydrin. Thus, a polyether, which is substantially diglycidyl etherof 2,2- bis(2,3-epoxypropoxyphenyl)propane is obtained by reactingbisphenol 2,2-bis(4-hydroxyphenyl)propane with an excess ofepichlorohydrin in an alkaline medium. Other polyhyrdric phenols thatcan be used for this purpose include resorcinol, catechol, hydroquinone,methyl resorcinol, or polynuclear phenols, such as2,2-bis(4-hydroxyphenyl)-butane, 4,4- dihydroxybenzophenone,bis(4-hydroxyphenyl) ethane, and l,5.-dihydronaphthalene.

Still a further group of the polyepoxides comprises the polyepoxypolyethers obtained by reacting, preferably in the presence of anacid-acting compound, such as hydrofluoric acid, one of theaforedescribed halogen-containing epoxides with a polyhydric alcohol,and subsequently treating the resulting product with an alkalinecomponent. Polyhydric alcohols that may be used for this purpose includeglycerol, propylene glycol, ethylene glycol, diethylene glycol butyleneglycol, hexanetriol, sorbitol, mannitol, pentanetriol, pentaerythritol,diand tripentaerythritol, polyglycerol, dulcitol, inositol,carbohydrates, methyltrimethylolpropane 2,6-octanedil,l,2,4,5,-tetrahydroxycyclohexane, 2-ethyl-hexanetriol-l,2,6, glycerolmethyl ether, glycerol allyl ether, polyvinyl alcohol and polyallylalcohol, and mixtures thereof. Such polyepoxides may be exemplified byglycerol triglycidyl ether, mannitol, tetraglycidyl ether and sorbitoltetraglycidyl ether.

A further group of the polyepoxides comprises the polyepoxy polyestersobtained by esterifying a polycarboxylic acid with an epoxy-containingalcohol, such as, for example, the diglycidyl ester of adipic acid, thediglycidyl ester of malonic acid, and the diglycidyl ester of succinicacid.

Typically, the benefits of the invention are obtained by blending thehardener with the epoxides, usually employing standard blendingequipment known in the art, together with any other adjuvants desired,and then when read for use in service, by activating the hardener. lngeneral, the amount of 5 hardener used will be at or near thestoichiometric amount required for the specific ingredients. Usually,this will range from about to 45 parts of hardener per 100 parts ofresin (phr). For the preferred compositions of the invention, this rangewill be about to 30 and most preferably, about phr.

The conditions of time and temperature used for cure ordinarily aspreviously stated, will vary from blend to blend. In general, however,elevated cure temperatures ranging from 130 C. to 170 C., and preferably140 to 160 C, will produce physically desirable resin products within 30minutes to 1 hours, and usually within 30 minutes. OF course, thesecures can be effected in the same attitude as the end use where thephysical conditions permit. Most preferably, the cures are effected by apreliminary gel period at a low curing temperature followed by storagefor a somewhat longer period at a more elevated temperature. Bestresults are obtained by an initial gelling at around 90 to 100 C.,followed by heating at around 130 to 170 C. for 30 minutes to 1 hour.Solid bisphenol A based resins are generally slower curing than liquidbisphenol A based resins and may require the use of chemicalaccelerators or less preferably, higher temperature or longer curetimes. It is not, under most circumstances, ordinarily desired to raisethe curing temperature to accelerate these times because in doing sothere is a tendency for the reaction mixture to gel too rapidly.Therefore, it is preferred to use such chemical accelerators asisoniazid, dicyandiamide, imidazole, and the like. These are usuallyemployed at levels from about 0.1 to 5 phr, and preferably 0.5 to 3 phr.Other adjuvants such as fillers, coloring agents and the like, typifiedby silica, pumice, pigments and the like, may also be used.

The products of the present invention are stable prior to cure forrelatively long periods of time under normal conditions. It is notunusual for the blend to remain latent or dormant for periods of 10months or more when stored at C. However, storage times longer than 3months at temperatures of 40C. and higher should be avoided.

The cured products obtained from the compositions of this invention findapplication in a variety of areas including hightemperature adhesives,electrical potting and coating applications and the like. Theiroutstanding dielectric properties together with good tensile andflexural properties make these materials eminently suitable forelectrical insulation applications. As such they are quite favorablycompared to aromatic amine-cured epoxides.

Certain of the latent hardener compounds of the present invention arenovel. As far as is known only 4,6-bis[(2-aminophenyl)carbamyl]isophthalic acid (i.e., R=2-aminophenyl in the formula above) is known,having been described in Chem. Abst. 64: 12807 D. All other componentswithin the general class above are new. They may be prepared byfollowing the procedure set forth in the above-noted reference makingthe appropriate substitution for the aminophenyl substituent-carryingreactant. For instance, in the illustrative example below, theappropriate R-containing compound corresponding to 1,2-diaminobenzene isreacted with pyromellitic acid dianhydride in a suitable inert solventsuch as dimethyl formamide, diemthylacetamide, and the like. Thereaction is exothermic and it is desirable to proceed at a temperaturebelow about 40 C, preferably between 20-35 C. The final compound is thenrecovered by standard techniques.

The following examples are illustrative of preferred embodiments of theinvention.

EXAMPLE 1 Twenty-nine parts by weight of 4.6 bis [(2-amino-phenyl)carbamyl] isophthalic acid are blended with 100 parts of a liquid epoxyresin prepared from bisphenol A and epichlorhydrin and having an epoxyvalue of 0.53 equivalents per 100 gm. on a three-roll mill at about 23C. until a smooth, pasty blend is obtained. This material can be curedat elevated temperatures in a short period of time, and has the abilityto retain that characteristic for over a year. This is demonstrated byobserving the amount of time required to effect gelling or hardening atthe indicated cure temperature. Such a gel-time test is as follows:

A cure plate is heated to 150:0.5 C. and coated with a thin film ofrelease agent.

-1.0 gmi0.1 gm. of test sample is spread lightly in a 2 2 S36E05 65 mcure plate with a back-and-forth movement using a metal spatula. Whenthe viscosity of the material increases, as noted by drag on thespatula, the spatula is removed. The point at which the material doesnot string but comes up in a rim when the spatula is lifted is the endpoint. The time from the start is noted,

Using this test, it is found that the initial gel 269 seconds at 150 C,for a 1 gm. batch.

At the end of 1 year, the batch prepared according to the aboveprocedure had a gel-time value at 150' C. of 226 seconds. This indicatesthat the blend cures within a reasonable time for period up to a year.

time is about EXAMPLE 11 A. A test blend prepared in accordance withExample 1 except that 20 parts of the acid are used instead of 29,yields a 30 gm. gel time (in a 25X150 mm. test tube immersed in an oil.bath) at 150 C. of 10 minutes for the initial blend and an 8.5 minutevalue after 3 months storage at 25 C. There is no substantial change inviscosity at 25 C. after 3 months (21,000 to 26,000 cps.).

B. Typically, gel times increase with decreasing test temperature. Thus,for the above blend, while initial gel time at 150 C. is 10 minutes; atC. it is 120 minutes. Other values are as follows:

Gel Temperature C. 11 0 (30 gram mix Cure Temperature C. Deflectiontemperature C.

*1. (Deflection temperature is the temperature required to deflect a SXAX slab of test material 0.010 under a load of 264 p.s.i. and atemperature gradient increase of 2 C./min. This is a measure ofthetherrnal relaxation behavior of the material with higher valuesindicating good thermal stability.

From the above, it can be seen that the optimum cure temperature is 150C. Best deflection temperature was obtained at 150 C. postcure for 2hours following the 90 C. gel period.

D. Material prepared in section A and gelled at 90 C. followed by 2hours cure at 150 C. had the following physical characteristics whentested at 25C. and 149 C.

EXAMPLE Ill The procedure example I is followed using the followingformulations: 7

Parts Methylene dianiline tetraepoxide 100 4,6 bis [(2-aminophenyl)carbamyllisophthalic acid 30 The smooth blend was then used as anadhesive in tensile shear strength tests by preparing k-inch overlapbonds in accordance with ASTM D-1002-64 for room temperature testing andMlL A-5090D for elevated temperature testing. Prior to testing, thematerial was cured for 20 minutes at 150 C., plus 1% minutes heat-uptime.

p.s.|. Tensile shear strength at 25 C. 1.139 Tensile shear strength atl49 C. 1,380 Tensile shear strength at 177 C. 1.550 Tensile shearstrength at 200 C. 1.1 70

EXAMPLE IV Following the procedure of example I, smooth blends areobtained using the following latent hardeners in the amount indicated inplace of the acid described in that example.

A. 4,6 bis [(4-methoxy-6-aminophenyl) carbamyl] isophthalic acid30phr.

EXAMPLE V 4,6 bis [(2-aminophenyl carbamyl)] isophthalic acid A solutionof 64.8 g. (0.6 mole) of 1,2-diaminobenze in 800 ml. dimethylformamideis prepared. To this stirring solution is added 67.4 g. (0.3 mole ofpyromellitic dianhydride incrementally at a rate to keep the exothermtemperature below 35+ C. The solution is stirred for 1 hour at roomtemperature after the additions are completed. The solvent is removed atreduced pressure (ca. 0.5 mm.) until the remaining solid is absolutelydry. The solid is pulverized in a blender and washed twice with 700 ml.acetone until the product is a yellow solid. It is then repulverized ina blender and air dried. The product is a gold-colored solid, mp. 245 C.Dec. of acid number 200-220 mg./g. The yield is 115 g.

EXAMPLE Vl 4,6-Bis (3,4-diaminoanisole carbamyl) isophthalic acid Thegeneral procedure used in example V is followed using 82.8 g. (0.6 mole)of 3,4-diaminoanisole and 67.4 g. (0.3 mole) of pyromelliticdianhydride. The product is a pale yellow solid with a decompositiontemperature of 275 C. and an acid number of 185-200 mg./g. The yield is50 g.

EXAMPLE Vll 4,6-Bis( 3-aminophenyl carbamyl) isophthalic acid Thegeneral procedure used in example V is followed using 64.8 g. (0.6 mole)of 1,3-diaminobenzene and 67.4 g. (0.3 mole) of pyromelliticdianhydride. The product is a yellowcolored solid, mp. 110 C. (dec.) ofacid number 190-200 mg./g. The yield is 140 g.

EXAMPLE Vlll 4,6-Bis( 3-a-aminoxylylenyl carbamyl) isophthalic acid Thegeneral procedure used in example V is followed using 81.7 (0.6 mole) of1,3-xylylene diamine and 67.4 g. (0.3 mole) of pyromellitic dianhydride.The sohdprgduidecomposes from 130-145 C. and has an acid number of150-180 mg./g. The yield is 145 g.

EXAMPLE IX carbamyl) isophthalic EXAMPLE- x 4,6-Bis(a-amino-p-methylcarbamyl) isophthalic acid The general procedure used in example V isfollowed using 102 g. (0.6 mole) of p-menthane diamine and 67.4 g. (0.3mole) of pyromellitic dianhydride. The product is a solid, mp. 250 C.(dec.) ofacid number 173 mg./g. The yield is 170 g.

EXAMPLE Xi A solution of 100 g. (0.48 mole) of Z-(p-aminophenyl)benzimidazole in 2,000 ml. of dimethylformamide is prepared. To thisstirring solution is added 50 g. (0.22 mole) of pyromellitic dianhydrideincrementally at a rate to keep the exotherm temperature below 35 C. Thesolution is stirred at 30 C. until a precipitate forms. The product isfiltered and washed twice with 50 ml. of dimethylformamide. The lightyellow, infusible solid has an acid number of 160 mg./g. The yield is 116 g.

What is claimed is:

l. A latent curing resin composition capable of being cured at elevatedtemperatures comprising a 1, 2 epoxy resin and a compound having theformula HOOC -COOH RNOO- -CONR wherein R is a substituted phenyl radicalof the formula or a substituted cyclohexyl radical of the formula

2. The composition of claim 1 wherein R is the substituted phenylradical and n is O.
 3. The composition of claim 2 wherein R1 is 2-aminoand R2 is hydrogen.